The present invention relates to chlorinated ultra low density polyethylene with excellent rubber-like properties. More particularly, it is concerned with chlorinated ultra low density polyethylene produced by chlorinating an ultra low density polyethylene which is produced by copolymerizing ethylene and an .alpha.-olefin by the use of a specific catalyst.
Heretofore, there has been employed as the starting polyethylene a high density and linear low-density polyethylene produced by a medium- and low-pressure process or a low density polyethylene produced by a high-pressure process.
It is widely known that chlorinated polyethylene with rubber-like properties is obtained by chlorinating an polyethylene or a copolymer of ethylene and an .alpha.-olefin. However, as such polyethylenes, which are principally a high-density polyethylene or a linear low-density polyethylene, are highly crystalline, it is necessary to introduce a substantially high proportion of chlorine into the polyethylene in order to produce a chlorinated polyethylene with rubber-like properties. On the other hand, the introduction of a high proportion of chlorine would not be desirable because of deterioration of the flexibility at low temperature possessed in nature by the polyethylene and possible evolution of a large amount of harmful gaseous substances such as gaseous chlorine although the oil resistance is improved.
Chlorinated products of .alpha.-olefin copolymer rubbers produced by using a solid catalyst containing vanadium such as ethylene-propylene copolymer rubber (EPR) and ethylene-propylene-nonconjugated diene copolymer rubber (EPDM), such copolymers being of excellent low-temperature properties but being disadvantageously of poor flowability and low tensile strength, also have disadvantages such as poor processability due to poor flowability, low tnesile strength and being too soft to be smoothly chlorinated despite of their good low-temperature properties.
Moreover, EPR and EPDM which are of good low-temperature properties but of poor heat resistance with a maximum peak temperature of below 100.degree. C. as determined by the differential scanning calorimetry disadvantageously afford chlorinated products also with poor heat resistance. Copolymers prepared by means of a vanadium catalyst, which have a much lower dynamic viscoelasticity (E') at 0.degree. C. as determined by the dynamic viscoelastic measurement than that of copolymers prepared by means of a titanium catalyst, produce chlorinated products of inferior heat resistance also with a lower dynamic viscoelasticity.
In addition, unlike the case in which a titanium catalyst is employed, polymers prepared by means of a vanadium-containing catalyst definitely need a catalyst-removing step because of a lower polymerizing activity and toxicity of vanadium.